Foundation Wall Question 1

[JC2021]

Hi all,

I am designing a foundation for a 200' X 100' steel building. The client would like to essentially be able to dig a trench around the perimeter of the building and pour it full of reinforced concrete. The columns are 28' center to center with factored vertical loads of 60k and max uplift due to wind of 25k, and max horizontal loads of 38k. I know the foundation will be at least 2' thick because that is his smallest bucket. He would also like the top of the wall to be 6" narrower at the top so he can rest the slab on it.

My question is: Do I analyze and reinforce this like a wall, or a beam, or possibly even a slab? I've been through ACI 318 over and over, but it doesn't seem to have anything that directly applies to this situation.

Thanks

 

[dik]

2' thick or 2' wide? What is the soil like? any idea of bearing pressures in the locale? Any frost issues? Can the foundation accommodate a little movement, like frost heave? 60K, say service load at 45K with 3ksf bearing is about 15 ft^2... x 2' wide is about 8' long which can be done with proper reinforcing... Columns have to be centred on the 2' width... check with a 'real' engineer in the area...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[KootK]

I'd be treating that like a 2' wide beam unless it is either very deep or very shallow.

 

[JC2021]

That's the direction I was leaning KootK. We're going to be about 3' deep for the frost layer. So I treat it like a 2'X3' continuous beam.

 

[HTURKAK]

So the width of grade / foundation beam is determined according to smallest bucket width.. If FGL is one foot above the grade, total depth should be in the range of 3-4 ft ?. What is the frost depth ? and moment ? Are the columns nominally pin connected?

I will suggest you, analyze ftg as the continuous beam supported on elastic foundation and provide tie reinf. at the SOG to resist tension and horizontal loads.

 

[JStructsteel]

We used to design them that way all the time for tilt up. We would leave it 8" down, they would form up the slab and pour to the exact needed dimensions. Always looked at it as a beam.